An upright vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head mounted on the main body and having a suction opening, and a motor-driven fan unit for drawing dirt-bearing air through the suction opening. The dirt-bearing air is conveyed to the separating apparatus so that dirt and dust can be separated from the air before the air is expelled to the atmosphere.
The suction opening is directed downwardly to face the floor surface to be cleaned. The separating apparatus can take the form of a filter, a filter bag or, as is known, a cyclonic arrangement. The present invention is not concerned with the nature of the separating apparatus and is therefore applicable to vacuum cleaners utilizing any of the above arrangements or another suitable separating apparatus.
A driven agitator, usually in the form of a brush bar, is supported in the cleaner head so as to protrude to a small extent from the suction opening. The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. The brush bar comprises an elongate cylindrical core bearing bristles which extend radially outward from the core. The brush bar may be driven by an air turbine or by an electric motor powered by a power supply derived from the main body of the cleaner. The brush bar may be driven by the motor via a drive belt, or may be driven directly by the motor, so as to rotate within the suction opening. Rotation of the brush bar causes the bristles to sweep along the surface of the carpet to be cleaned to loosen dirt and dust, and pick up debris. The suction of air causes air to flow underneath the sole plate and around the brush bar to help lift the dirt and dust from the surface of the carpet and then carry it from the suction opening through the cleaner head towards the separating apparatus.
The suction opening is generally formed in a sole plate which faces the floor surface to be cleaned. To assist the maneuvering of the sole plate over a hard floor surface, it is known to provide the sole plate with wheels for engaging the hard floor surface. These wheels may also serve to raise the brush bar above the hard floor surface so that the bristles of the brush bar do not come into contact with the hard floor surface. When the cleaner head is located on a carpeted floor surface, these wheels sink between the fibres of the floor surface so that the bristles of the brush bar are able to come into contact with, and therefore agitate, the fibres of the floor surface. However, the location of the wheels between fibres of the carpet can impair sideways movement of the cleaner head over the carpeted floor surface.